I. Field of the Invention
The present invention relates generally to a fuel control system for internal combustion engines and, more particularly, to a fuel control system during an engine start condition.
II. Description of Related Art
Most modern day internal combustion engines of the type used in automotive vehicles are four-cycle engines having a plurality of internal combustion chambers. An intake manifold has one end open to the throttle and its other end open to the internal combustion chamber via the throttle intake valves. During a warm engine condition, a multipoint fuel injector associated with each of the internal combustion chambers provides fuel to its associated internal combustion chamber. The activation of each multipoint fuel injector is controlled by a processing circuit also known as an electronic control unit (ECU).
During the engine operation, pistons contained within the combustion chambers are drivingly connected to a crankshaft so that reciprocation of the pistons within their respective chambers rotatably drive the engine crankshaft. Similarly, during engine operation, an engine camshaft controls the operation, i.e. opening and closing, of the engine intake valves. A camshaft is also associated with the engine exhaust valves to enable the combustion products from the combustion chamber to be exhausted from the engine.
For a four-cycle internal combustion engine, each combustion chamber in the engine undergoes four cylinder strokes during one complete engine cycle. These strokes are the intake stroke in which a fuel/air mixture is inducted into the cylinder, a compression stroke in which the air/fuel mixture is compressed, a power stroke in which the air/fuel mixture is ignited, and an exhaust stroke in which the combustion products are exhausted from the engine cylinder. Furthermore, in a multiple combustion chamber engine of the type used in automotive engines, the individual cylinder strokes are staggered between the various combustion chambers.
Since the engine undergoes four engine strokes per complete engine cycle, each cylinder in each combustion chamber undergoes two reciprocations within its combustion chamber per engine cycle. Consequently, the crankshaft rotates at a rotational speed equal to twice the rotational speed of the camshaft. Additionally, when any piston is at top dead center in its associated combustion chamber, the engine cycle for that combustion chamber may be either immediately after the compression cycle or immediately after the exhaust cycle.
In order for the ECU to determine engine synchronization, i.e. the position and cycle of each combustion chamber in the engine, the previously known internal combustion engines have utilized both a crankshaft and camshaft position sensor. The crankshaft position sensor provides an output signal to the ECU representative of the angular position of the crankshaft while, similarly, the camshaft sensor provides an output signal representative of the angular position of the camshaft. Typically, a gear wheel having one or more missing teeth is secured to both the crankshaft as well as to the camshaft. A sensor then detects the absence of the tooth on the crankshaft gear wheel or camshaft gear wheel so that the sensors generate an output signal to the ECU. Furthermore, complete synchronization of the engine until an output signal from both the crankshaft sensor and the camshaft sensor, or the absence of an output signal from the camshaft sensor which would otherwise be expected, is received by the ECU.
Once synchronization is determined by the ECU, the ECU then generates the appropriate output signals to the multipoint fuel injectors, spark plugs, and the like in order to achieve the desired engine operation for the vehicle.
Although engine operation by the ECU during a steady state operating condition for the internal combustion engine is straightforward, special problems arise during an engine start condition. More specifically, during an engine start condition and during the synchronization period, i.e. before the ECU determines the position of the crankshaft and camshaft, spark timing is not possible since the spark must be generated at very specific crank angles. Conversely, the actual injection timing of the fuel into the engine is less critical provided that the fuel injection precedes the spark by at least one-half crank revolution since the intake valves are closed during the compression stroke at the end of the intake stroke.
Additionally, in order to ensure fast engine startup, it is necessary to provide a relatively large amount of fuel to the engine during a startup condition. However, the injection of excess fuel to the engine which is uncombusted disadvantageously results in increased engine emissions. Such increased engine emissions may not meet governmental emission level requirements.
Consequently, in order to provide fuel to the engine during a startup condition and yet minimize undesirable engine emissions, there have been previously known cold start fuel injectors which provide the fuel charge to several or all of the combustion chambers for the engine during an engine startup condition. The cold start fuel injector injects sufficient fuel into a cold start fuel passageway open at its outlet to the air intake passageway to provide the fuel charge to the engine during engine warm up. As the engine warms up, the cold start fuel injector is gradually deactivated while, simultaneously, the multipoint fuel injectors are gradually activated in order to provide a smooth transition between the cold start fuel injector and the multipoint fuel injectors.
These previously known fuel control systems for the engines during engine startup, however, have suffered from a number of disadvantages. One such disadvantage is that it is necessary to provide an overly rich fuel mixture to the engine during a cold start engine condition in order to ensure proper engine starting. Many of the previously known systems which have a cold start fuel injector utilize electric heaters within the cold start fuel passageway to vaporize the fuel prior to its induction into the internal combustion engine. However, because it is necessary to provide a relatively large quantity of fuel in order to obtain the overly rich combustion charge to the engine combustion chambers to ensure smooth engine starting, in many cases, the fuel injected by the cold start fuel injector overly cools the electric heater. When this happens, unvaporized fuel is inducted into the engine combustion chambers during engine startup. Such unvaporized fuel disadvantageously increases noxious emissions from the engine in excess of those required by governmental emission regulations.
A still further disadvantage of these previously known fuel management systems during engine startup is that typically the cold start fuel injector is only activated once the engine attains a certain rotational speed, e.g. 70–100 rpm. When that rotational speed is obtained, the ECU begins activation of the cold start fuel injector. However, after this rotational speed is attained during engine cranking, the internal combustion engine must induct all of the air from the cold start fuel passageway before the actual air/fuel mixture from the cold start fuel injector actually reaches the internal combustion chambers of the engine and thus before actual fuel combustion can begin. This delay is known as the cold start fuel injector transport delay. In many cases, the delay can extend as long as eight combustion cycles for the engine.
A still further disadvantage associated with the cold start fuel injector transport delay is that, when the fuel charge from the cold start fuel passageway actually reaches the engine combustion chambers, only a partial air/fuel mixture is inducted into the engine combustion chamber during the first initial intake cycles for the engine. This partial fuel charge is typically insufficient to achieve engine combustion in the combustion chamber thus resulting in an uncombusted fuel charge in the engine exhaust. Such uncombusted fuel causes unacceptable engine emissions.